Fiber-reinforced composite materials including a resin and reinforcing fibers in combination (FRP) have excellent lightweightness, rigidity, impact resistance and the like, and therefore, these materials are used in various applications. Particularly, carbon fiber-reinforced composite materials, which are lightweight and have high strength and high rigidity, are used in a large variety of fields such as sports/leisure applications such as fishing rods and golf shafts, automobile applications, and aircraft applications. Furthermore, in recent years, carbon fiber-reinforced composite materials are also used as housings for electronic/electric instruments such as laptop computers, by making advantages of the mechanical characteristics of carbon fiber-reinforced composite materials as well as electromagnetic wave shielding properties of carbon fibers.
Depending on the application, flame retardant performance is demanded for fiber-reinforced composite materials. For example, in a case in which fiber-reinforced composite materials are used for electronic/electric instruments, structural bodies for aircrafts and the like, since ignition caused by heat generation may cause a fire, flame retardant performance is required.
Regarding a method for making a fiber-reinforced composite material flame-retardant, methods of adding a brominated epoxy resin to a matrix resin composition have been widely used. However, in recent years, as a method for making a fiber-reinforced composite material flame-retardant in lieu of the addition of a brominated epoxy resin, an epoxy resin composition including a phosphorus-based flame retardant has come to be used, in consideration of the burden exerted on the human body or environment by the substances generated upon combustion of a resin composition including a halogen. Regarding an epoxy resin composition including a phosphorus-based flame retardant, for example, the epoxy resin compositions described in Patent Literatures 1 and 2 have been suggested. Furthermore, in regard to such flame-retardant epoxy resin compositions, for example, dicyandiamide and imidazole may be used in combination as curing agents (see Patent Literatures 1 to 3).